Hybrid type network



Aug. 23, 1960 A. ALFORD HYBRID TYPE NE'rwoRK 3 Sheets-Sheet 1 Filed NOV.21, 1956 Aug. 23, 1960 A, ALFORD HYBRID TYPE NETWORK 3 Sheets-Sheet 2Filed NOV. 2l, 1956 E V m Allg. 23, 1960 A, ALFORD 2,950,449

HYBRID TYPE NETWORK Filed NOV. 21, 1956 3 Sheets-Sheet 5 PARALLEL BRANCHSIDE BRANCH I SERIES BRANCH FIG.7

IN V EN TOR.

ANDREW ALFORD ATTORNEYS United States Patent HYBRID TYPE NETWORK AndrewAlford, Winchester, Mass. (299 Atlantic Ave., Boston, Mass.)

Filed Nov. 21, 1956, Ser. No. 623,560

4 Claims. (Cl. S33- 11) The present invention relates to a hybrid typecircuit particularly designed to handle wide bands of frequencies.

In hybrid structures utilized previously, the range of frequencies overwhich they would accurately operate was severely limited. Ordinarilyhybrids have a maximum range of frequency in the ratio of 2 to 1; as forexample, from 120 to 240 megacycles, or 480 megacycles to 960megacycles. In many instances, much wider ranges are necessary; as forexample, a range of 200 to 900 megacycles, or a 41/2 to 1 ratio. Thisrequirement of a wide frequency range capacity has often necessitatedthe use of several interchangeable hybrids, with a single electronicinstrument. Such multiplicity is not only economically undesirable, butalso results in unnecessary delays in the substitution of one hybrid foranother.

yIn the hybrids previously utilized for frequencies of 40 megacycles andup, for example, the particular frequency range for which the hybrid isdesigned is determinative of its overall size with the lowest frequencydetermining the maximum size of the hybrid. For example, in hybridsdesigned to be used with frequencies of 40 megacycles, the `overalllength of the hybrid would be approximately six feet long. A unit ofsuch a length often poses major problems in instrument design and inaddition, increases the cost not only of the hybrids, but also ofassociated structures.

These principal diiculties of hybrids previously known are overcome inthe design of the present invention which provides a structure havingthe hybrid-like characteristics of previously known structures. Thepresent invention provides a structure which is capable of handlingfrequencies over a range of approximately l5 to l or perhaps greater ina structure having an overall size substantially smaller than the sizeof hybrids for corresponding frequencies previously known. According tothe invention, four terminal pairs are provided, each having a groundedor low and ungrounded or high terminal with the grounded terminalsconnected to common conducting means. A rst of the ungrounded terminalsis connected to the junction of iirst and second seriallyconnectedresistors. Means, such as a balun, `are provided for converting anunbalanced signal on a second of the ungrounded terminals to a balancedsignal which is applied across the serialiy-connected resistors. Thethird and fourth ungrounded terminals are connected to the rst andsecond resistors respectively at the ends away from their junction. Thelatter two terminals are referred to as side terminals l and il,respectively. The iirst terminal is referred to as the P or parallelfeed input terminal because energy applied to this terminal is deliveredto loads connected to the side terminals over parallel paths. The secondterminal is referred toas the S or series feed input terminal becauseenergy applied to this terminal is delivered to loads connected to theside terminals over a path effectively coupling said loads in series.

If the'twoY resistors Yare of equal value and the loads Y 2,950,449Patented Aug. 23, 1960 connected to the side terminals are equal, theseries feed input is isolated from the parallel feed input.

In a preferred embodiment of the invention, the balun comprises a coiledcoaxial transmission line beside a coiled conductor essentially themirror image of the coiled coaxial transmission line with the coils andthe resistors symmetrically arranged within a conducting shield whichforms the common conducting means. A balun formed in this mannerpresents a high impedance path to energy `incident at the parallel feedinput so that nearly all such energy is `delivered to the side terminalsover parallel paths. By connecting one end of the coiled transmissionline center conductor lto the series feed input terminal, the other end-to one of the side terminals and the outer conductor of the coiledtransmission line at said other end to the other side terminal, a lowimpedance path is provided for transferring energy from the series feedinput to loads connected to the side terminals over a series path. Theouter conductor is connected between ground and said other side terminalwhile the coiled conductor is connected between ground Vand said oneside terminal.

The outer conductors of all coaxial terminals are connected to the metalshield of the network. The metal shield may be a closed metal enclosureor alternatively comprise only two parallel metal plates spaced at adistance which is small, for example 1/2 `inch in comparison with theirother dimensions, for example, 6 inches by 6 inches.

The previously enumerated objects and advantages of the presentinvention will be more clearly understood when considered in connectionwith 'a specific embodiment of the invention, as is illustrated in theaccompanying drawings, in which:

Figure l is a top plan view of the invention with upper plates removedFigure 2 is a cross sectional view taken substantially along the line 22 of Figure 1.

Figure 3 is a perspective assembled view of the invention.

Figure 4 is a perspective View of the invention with portions removed.

Figure 5 is also a perspective view of the invention with furtherportions removed;

Figure 6 is a detail of Figure l; and

Figure 7 is a schematic representation of a preferred embodiment of theinvention.

In considering the specic embodiment of the present invention, asillustrated in the accompanying drawings,

it should be understood that the description is merely illustrative ofthe invention and is not conned to the specific details as hereinafterenumerated in the specication.

In the hybrid of the present invention, there are provided fourterminals, `for convenience respectively labelled, terminals, S, I, P,and ll. These which are illustrated at type N, coaxial cable terminalshave their inner conductors connected respectively to strip members ofcopper 5, 6, 7 and 8. These strip members extend inwardly and aresupported by and secured to a suitable dielectric material, such aspreferably the substantially rectangular member 9. The surface of thecopper strips 5, 6, 7 and 8 and the dielectric material 9 arecoextensive and are in face to face relation with a second dielectricmember 10. This second dielectric member 10, preferably has an outlineindicated by numeral 14. The outer surfaces of the dielectric members 9and 10 are covered with conductive members or coatings 11 and 12 formedof a layer or sheet of copper. The conductive members 11 and 12 areinterconnected by a series of through-bolts or rivets 13, therebyforming with'the strips 5, 6, 7 andS, and the conductive sheets 11 and12, a coaxial-like conductor line system. At the inner end of the strip5, there is positioneda ground plate 15, suitably anchored to thedielectric material and electrically connected to the plates 11 and 12.Connected tothis -ground plate 15 are Vthe rst and second innertransmission lines 17 and r16, with the outer conductor Yofthe line 17being connected at one end to the ground member 15 and the innerinsulated conductor 19 beingY connected to the end 18 of the strip 5.The. inner conductor 19 of the line 17 is insulated from the outerconductor by dielectric coaxial material which may consist of materialsuch as Teon. The other end of the inner conductor 19 projects outwardlyof the other end of the outer conductor of this coaxial line 17 and isconnectedto the other end of the line 16 at point n. `The ends 20 and 21of the lines 17 and 16 respectively are respectively connected to theungroundedV conductive blocks 22 and 23 by solder or other suitablematerial. These blocks 22 and 23 are insulated one from the other. Apair of resistors 2'4 and 25 at one end are connected one each to theterminals or blocks 22 and Y23.A The other ends of these-resistors whichshould preferably be equal in size, are connected together at the innerend 27 of the strip 7 in turn connec'ted to the inner conductor of thecoaxial terminal P.

An opening 30 of rectangular shape is provided in the dielectric members9 and 10 and conductive members 11 and 12. The lines 16 and 17 arepositioned within this opening. A recess 31 is also provided in the-dielectricV plate 9 to receive the resistors 24 and 25. A recess v50may be lformed in the dielectric member 10 in the area covering theseresistors 24 and 25 and the blocks 22 and 23. A conductive coveringmember is positioned over these openings and may consist of therectangular caps 32 and 33 positioned respectively on either side of theconductive members 11 and 12. These caps 32 and 33 may be securedtogether and in position by throughbolts or the like which pass throughopenings indicated at 34.

The type N coaxial line connector 40 is secured by screws or suitablemeans to the conductive member 11 and projects normally from it with theouter conductor of 'this connector being connected electrically to themembers 11 and 12, and with the inner conductor of the .connector beingelectrically connected to the strip 7, but

insulated from the members 11 and 12. Terminals I and II and S, each mayhave connected to them aV typey N connector 41, with the connector beingmounted upon a removable block member 44. These block members areprovided with shoulder sections 45 adapted to fit over and nestleagainst the dielectric member 9 over the stripsV 5, 6 and 8. The blockmembers tit snugly against the walls of the dielectric member 10 and aresubstantially continuous with it. Each side of the block member has ametallic coat or conductive member with a parallel metallic stripbetween them. The outer or upper surface facing away from the dielectricmember 9 on each block 44, is provided with the conductive member 46 ofcopper with this member 46 being electrically connected to the outerconductors of the connectors 41. The second conductive member 100 on theother side of the block is electrically connected to the plate 11 by acoupling plate 101. The screws 13 couple members 46, 100 and alsopartially secure connector 41 to member 46. Other screws 13 secure plate11 and members 101 and 46 in sandwich fashion. The inner Vconductors ofthe connectors 41 are each connected to a strip of conductive material47 of copper which rests in face to face relationship with one of thekrespective strips 5, `6 and 8, beyond the shoulder section of the blockand form therewith continuous connections from the inner conductors ofthe connectors 41 to the inner end of the respective terminals withwhich the conductors 41 are connected.

The outer plates 46 Yare connected electrically to the member 12 bymeans .of Veonductive coupling plates 48Y 4 which are suitably securedby screws 49 or the like to the plate 12 and the plates 46.

In the operation of the present invention, a radio frequency potentialmay be applied to the terminal S from a suitable power source. This R.F.power is fed through the line `17 and together with the shuntedconnection to line 16 results in equal and opposite voltages beingapplied at points m and n of the blocks 22, 23, provided equal loadsare'connected to the terminals I and II. Under these conditions, equaland opposite voltages are supplied to resistors 24 and 25 so that at thejunction of these resistors, and therefore, at terminal P, there will beno voltage. Similarly, by the Reciprocity Theorem, a voltage applied toterminal P will resultV in no voltage at terminal S provided terminals Iand II have equal loads connected to them. In the event that the loadsat terminals I and II are unequal, a voltage will appear at theterminalP whenterminal S is energized or vice versa. The voltage appearing atthe output being related to the difference between the two loads.

By using -a standard load at one ofthe terminals I or II and anunknownirnpedance at the other comprising for example both a resistive`and reactive component, the phase and the magnitude of the voltageyappearing at the output terminals are found to be related to therelation between the unknown impedance, and the standard load. Bycomparing this voltage at the output terminal with a reference voltageobtained from the input terminal, a measure of the unknown impedance maybe obtained.

From the foregoing it will be clear that the present inventionfunctioning as a hybrid is adapted for use as an impedance measuringdevice which has particular utility because of its reduced size and widefrequency range.

The lines 16 and =17 of the present invention are designed to provide ashigh an impedance between points m and n as possible consonant withtheoperatonal frequency range.

It is found that the overall unparalleled length of each coil should bekept somewhat shorter than a half wavelength of the highest frequencybut of the same order of magnitude `unless a magnetic core is used inwhich case the length should be decreased depending upon the increas'einthe ilux.

The coiled outer conductors 17, 16, constitute a length of balancedtransmission line which is effectively shunted across blocks 22, 23. Thefar end of the balanced transmission line is short circuited by metalstrip 15. The impedance looking into the balanced line 16, 17, isapproximately equal to -its characteristic impedance 200 multiplied bythe tangent of its eiective electrical length expressed in electricaldegrees. It is found that the charteristic impedance of a coiled line isgreater than the rcharacteristic impedance of an uncoiled line. It isalso found that the electrical length of la coiled line is at leastroughly equal to the uncoiled length of the helix. Because thecharacteristic impedance of the coiled line is high, even a relativelyshort length, 0 (in electrical degrees) results is a high reactiveimpedance 200 tan 6 being shunted across block 22, 23. When theimpedance of the shunted coiled line is high, the impedance seen lookinginto terminal S is closer to the idealized condition in which onlyresistors 24, 25 and the loads connected to terminalsV I and -II at Pare in the circuit. Thus the circuit achieved by using the arrangementof this invention approximates a bridge circuit which has been made tooperate with high -accuracy lat frequencies as high as 1000 megacycles.

Another embodiment of the invention contemplates removal of thedielectric material within the plates or shields except for supportingportions, and also complete enclosure of the internal components with Iametallic box rather than the parallel plates forming shields.

Referring to Fig. 7, there :is shown a schematic representation of theembodiment of the invention described J Tajinabove. Reference symbolsidentifying elements in the other portions of the drawings designatecorresponding parts of the schematic representation. A signal applied tothe series feed input branch between ground and the inner conductor 19of the coaxial transmission line 17 is converted into a signal which isbalanced with respect to ground between conducting bars 22 and 23. 1fthe loads connected to side terminals I and Il are equal and resistors24 and 25 are the same, the current to ground through each of the latterresistors is of the same magnitude but of opposite sense. As a result,the potential at junction 27 corresponds to ground potential. Anunbalance in the loads connected between each side terminal and groundis indicated by a deviation in the potential on junction 27, the Pterminal, from ground potential.

The side terminal loads are eectively energized in series from a sourceconnected to the S input, for energy travels from the outer conductorconnected to bar 22;, through the load connected between side terminal Iand ground, through the load connected between ground and side terminalII and through bar 23 to the inner conductor 19. Energy from a sourceconnected to the P input is delivered to the side terminal loads throughparallel paths respectively including resistors 24 and 25.

There has been described a network which exhibits hybrid properties overan exceptionally wide frequency range. It is apparent that those skilledin the art may now make numerous modifications of and departures fromthe speciiic embodiments described herein without departing from theinventive concepts. Consequently, the invention is to be construed aslimited only by the spirit and scope of the appended claims.

Having now described my invention, I claim:

l. An electrical network exhibiting hybrid properties comprising, fourterminal pairs each having high and low terminals with the low terminalsconductively interconnected, iirst and second resistors connected inseries, a rst of said high terminals being connected to the junction ofsaid serially-connected resistors, a second and third of said highterminals being connected to the ends of said rst and second resistorsrespectively away from said junction, and means for converting anunbalanced signal on the fourth of said high terminals into a balancedsignal which is applied across said serially-connected resistors, saidmeans providing an impedance between each of said second and thirdterminal pairs and said fourth terminal pair higher than that of saidseriallyconnected resistors.

2. An electrical network in accordance with claim 1 wherein said meanscomprises, a coiled coaxial transmission line having an inner and outerconductor with the inner conductor connected between said third andfourth high terminals and the outer conductor connected between saidconductively interconnected low terminals and said second high terminal,and a coiled conductor beside and substantially the mirror image of saidouter conductor, said coiled conductor being connected between saidconductively interconnected low terminals and said third high terminal.

3. An electrical network in accordance with claim 2 wherein the meansconductively interconnecting said low terminals includes a conductingshield symmetrically surrounding said resistors, said coiled coaxialtransmission line and said coiled conductor.

4. An electrical network in accordance with claim 3 wherein saidresistors are substantially equal.

References Cited in the file of this patent UNTTED STATES PATENTS1,371,471 Cohen Mar. 15, 1921 2,594,167 Herold Apr. 22, 1952 2,769,146Alford Oct. 30, 1956 FOREIGN PATENTS 724,131 Germany wwwwwww Aug. 19,1942

